1. Field of the Invention
This invention relates to bubble domain lattices and more particularly to an improved bubble domain lattice structure.
2. Brief Description of Prior Art
Bubble domains and stripe domains arranged in a lattice are described in copending U.S. patent application Ser. No. 395,336 filed on Sept. 7, 1973 now abandoned and assigned to the assignee of the present invention. As described therein, the bubble domain lattice consists of a plurality of rows and columns of bubble domains and/or domain stripes which occupy a spatial arrangement which is determined to a substantial extent by the interaction between the bubbles. A bubble lattice initialization method is described in copending U.S. Patent application Ser. No. 517,990 filed on Oct. 25, 1974 now U.S. Pat. No. 3,953,842 and assigned to the assignee of the present invention. As described therein the method provides an initial lattice containing a plurality of rows of substantially perfect parallel stripe domains and bubble domains. The aforementioned applications are incorporated herewith by reference thereto.
It has been observed that several problems exist in the formation and operation of a bubble lattice device. One such problem occurs during the translation of bubbles in the access column from and to the input and output ports respectively. The current that is applied in the conductor pattern to move the bubbles in the access column has a tendency to also move the bubbles in the adjacent columns by an amount which is sufficient to disturb the integrity of the lattice.
Another problem pertains to obtaining a particular number of rows in the bubble lattice. The number of rows of bubbles and/or stripes domains in a lattice in a given area depends to a large extent on magnetic material parameters which are determined by the chemical composition and the growth conditions of the bubble material. For example, to obtain a lattice having 28 rows of bubble domains in a given space on a garnet film, it is necessary to closely control the chemical composition of the garnet film. Unless the chemical composition is closely controlled the number of rows in this example can vary quite easily from, for example, 27 to 32 rows. As a result it is necessary to closely control the material parameters to obtain the same number of rows with different films in a given area.
Still another problem that has been observed deals with the translation of the bubbles laterally in the rows. Bubbles having a S=0 state, that is, where there is one pair of Bloch lines in the walls of the domain, move in a direction of an applied field gradient while bubbles having a S=1 state, that is, when there are not Bloch lines in the wall of the domain, move at an angle to the gradient. Since the conductor lines used to provide the lateral propagation or movement of the bubbles are parallel to the columns and are not perpendicular to the bubble rows, both the S=0 and the S=1 state bubbles may have a component of force which is not in the direction of translation, i.e., the horizontal direction of the rows. This force may, at times, cause one or more of the bubbles to sway or deviate from the horizontal direction.
Another problem is observed during or after the formation of a substantially perfect array of parallel stripe domains. It has been observed that on occasion the stripes that are formed stripe out in a direction which is perpendicular to the conductor rather than along the horizontal direction of the row. These difficulties occur due to the magnetostatic interactions between stripes and bubbles in the adjacent column and because the gradient being applied is in the direction perpendicular to the conductor when the current is applied to it.